(a) Field of the Invention
The invention relates Lo a protein fraction with high functionality, in particular high gelling and high solubility properties, and to a process for obtaining same.
(b) Description of Prior Art
The common gelling ingredients of foods are carbohydrates and proteins. Among proteins, gelatin and whey proteins are common gelling proteins from animal sources while soybean proteins are the common gelling proteins from plant sources. The diversity of food applications for gelling proteins requires proteins having different molecular structures which will determine the particular characteristics of the gel.
Heat-induced gelation is the common technique for food gelling applications involving proteins such as whey proteins and soybean proteins. Heat-induced gelation of whey proteins has been extensively reported. The ability of whey protein to form a gel at room temperature, after a pre-heat treatment, has also been reported (this phenomena is called cold-set gelation).
Few reports have been published on cold-set gelation. These mainly reported the effects of preheat treatments or denaturation levels on rheological properties of cold-set gels. Results consistently showed that more severe preheat treatments led to higher gel strength or shear stress. The strength or shear stress of gels was also dependent on added salt concentration in the post-denaturation step.
Cold-set gelation of whey proteins requires the initial preheat step to denature the whey proteins, followed by an incubation with such additives as salts, acidulants, or proteases. Cold set gelation has only been observed with whey proteins.
Cold-set gelation has potential applications in the food industry, in various foods, such as in surimi, pressed ham, spreads and bakery products.
Therefore, it would be highly desirable to be provided with a high-gelling protein with cold-set gelation abilities as a substitute for cold set whey proteins such as for non-dairy applications.
One aim of the present invention is to provide a cold-set gelling protein extracted from ground defatted soybean which forms strong protein gels and which has high solubility properties.
Another aim of the present invention is to provide a method for extracting such gelling protein.
In accordance with the present invention there is provided a process for obtaining a gelling protein from defatted soybean. The process comprises the steps of:
(i) extracting proteins from ground defatted soybean with an alkaline solution; and
(ii) precipitating the high gelling protein from proteins extracted in step (i) by cryoprecipitation.
The process may optionally further comprise before step (ii) the step of:
a) centrifuging the alkaline solution for obtaining a clarified supernatant containing the gelling protein.
The process preferably further comprises after step (ii), the step of:
(iii) isolating the gelling protein from step (ii).
The gelling protein may be isolated by a centrifugation after the cryoprecipitation for obtaining a pellet containing the gelling protein, and isolating the pellet.
The process may preferably further comprise after step (iii) the step of:
(iv) isoelectric precipitating of an alkaline solution obtained after the isolating of step (iii).
The isoelectric precipitating may optionally comprise a step of:
(v) adjusting the alkaline solution obtained after the isolating of step (iii) to a pH of about 4.5.
In a preferred embodiment, the process may further comprise after the step (iv) of isoelectric precipitating, a step of separation of a protein isolate for use in food industries and a supernatant containing oligosaccharides. The supernatant containing oligosaccharides is preferably recycled and reused in a further step (i) of the process for obtaining a gelling protein. The oligosaccharides may be recovered from the supernatant containing oligosaccharides after being recycled and reused.
In accordance with the present invention there is also provided a process for producing a cold-set gel comprising a gelling protein obtained by the process described above. The process comprises the steps of:
i) making an aqueous dispersion of the gelling protein;
ii) heating the dispersion to 60 to 90xc2x0 C.;
iii) adding a salt to the dispersion of step ii); and
iv) allowing for the dispersion of step iii) to set.
The salt added in step iii) is preferably selected from the group consisting of calcium chloride, sodium chloride, magnesium chloride, calcium sulfate, and magnesium sulfate.
In accordance with the present invention, there is also provided a gelling protein obtained with the process of the present invention. The gelling protein may be induced to gel by cold-set gelation.
In a further embodiment of the present invention, there is also provided a gel comprising the gelling protein of the present invention, in which the gel is induced by cold-set gelation of a solution comprising the gelling protein.
The protein of the present invention forms strong gels of concentrations similar to, or lower, than those required for gels from whey protein concentrates or other soybean protein preparations. These gels maintain good gelling characteristics during storage. These high gelling and high solubility properties make the protein of the present invention a suitable substitute for situations where non-dairy protein products are required and for fortifying both soy-based products such as soymilk and tofu as well as non soy-based protein food products.